Continuous and scalable 3d nanoprinting

ABSTRACT

A rapidly printing 3D nanostructures arrangement, comprising a first photonic source configured to provide photoinitiation energy to a polymer medium via a dynamic light spatial modulator to an excited state to initiate polymerization, a second photonic source configured to selectively provide inhibition energy to the polymerized medium to a depleted state to inhibit polymerization thereby generating a dead zone below a growth zone, the dead zone allows continuous 3D polymerization.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present patent application is a divisional of U.S. application Ser.No. 15/652,105 filed Jul. 17, 2017 which is related to and claims thepriority benefit of U.S. Provisional Patent Application Ser. No.62/362,868, filed Jul. 15, 2016, the contents of which is herebyincorporated by reference in its entirety into the present disclosure.

TECHNICAL FIELD

The present application relates to three-dimensional printing, and inparticular, continuous three-dimensional printing capable of producingnanoscale structures.

BACKGROUND

This section introduces aspects that may help facilitate a betterunderstanding of the disclosure. Accordingly, these statements are to beread in this light and are not to be understood as admissions about whatis or is not prior art.

Recently, there has been growing commercial interest inthree-dimensional (3D) printing (also known as additive manufacturing)for rapid prototyping and other purposes. Additive manufacturing toolsdeposit or extrude material in a layer-by-layer fashion to generatethree-dimensional (3D) objects. 3D printing can advantageously generateand rapidly prototype objects that are conceptualized on a computer orscanned from an external object. There are many examples including thepopular MAKERBOT (New York, N.Y.), which extrudes molten polymers in alayer-by-layer fashion until a 3D part is complete.

Additive manufacturing is a promising technique for applications rangingfrom product visualization to on-demand 3D printing of engineeringparts. In conventional additive or three-dimensional fabricationtechniques, construction of a three-dimensional object is performed in astep-wise or layer-by-layer manner. In particular, layer formation isperformed through solidification of a photocurable resin under theaction of visible or UV light irradiation. Two techniques are known: onein which new layers are formed at the top surface of the growing object;the other in which new layers are formed at the bottom surface of thegrowing object. In either case, the current state-of-the-art in most 3Dprinting is, in fact, the repetitive printing of 2-dimensional objects.

In a typical 3D fabrication process, new layers are formed at the topsurface of a growing object, then after each irradiation step the objectunder construction is lowered into the resin “pool,” a new layer ofresin is coated on top, and a new irradiation step takes place. An earlyexample of such a technique is given in Hull, U.S. Pat. No. 5,236,637 toHull (e.g., FIG. 3 of the '637 patent). A disadvantage of such “topdown” techniques is the need to submerge the growing object in a(potentially deep) pool of liquid resin and reconstitute a preciseoverlayer of liquid resin, thus slowing down the growth process.

A recent breakthrough has dramatically improved the speed of additivemanufacturing. As seen in U.S. Pat. No. 9,205,601 to Desimone et al.,this technique demonstrates the fabrication of monolithic polymeric 3Dparts up to tens of centimeters in size with feature resolutions below100 μm. FIG. 1 provides a schematic of the arrangement disclosed in the'601 patent. These complex 3D parts were drawn out of the resin througha continuous polymerization process at the interface between thefabricated (polymerized) part and the liquid resin. A key technology isthe use of an oxygen-permeable window located directly below theultraviolet image projection plane of photopolymerization. Thisoxygen-permeable window generates a dead zone where photopolymerizationis inhibited by oxygen between the window and the polymerizing part;therefore the liquid resin can be continuously fed for continuouspolymerization. As a result, 3D parts are fabricated at rates ofhundreds of millimeters per hour, and the entire fabrication processtakes minutes as opposed to many hours. Such a rapid 3D manufacturingprocess has attracted huge commercial interests as it provides for acomplete shift in paradigm and speed relative to other commercial 3Dprinting systems.

3D nanostructures, because of their unique properties at nanoscale,promise to be useful in myriad applications including efficient solarenergy conversion, catalysts for fuel cells and hydrogeneration, energystorage, clean water production, and medicine. Some nanomanufacturingefforts employed self-assembly methods to produce 3D nanostructures.Although these 3D nanostructures provided possible solutions for some ofthe aforementioned applications, it is often desirable to developmethods for fabricating geometrically and structurally well-defined 3Dnanostructures in order to realize the full potentials of the 3Dnanostructures and to do so in a high-throughput manner. One method thatallows for 3D nanostructure fabrication is laser-based polymerization,which has been utilized for producing photonic devices, micromechanicaldevices for drug delivery, platforms for tissue engineering and cellculture, and microscale machines (e.g., micro-turbines and micro-pumps).However, the current laser-based 3D nanofabrication processes arepoint-by-point processes and, thus, extremely slow.

The process disclosed in the '601 patent provides a groundbreakingtechnology to manufacture large, microstructured parts; however there isstill no high-throughput solution to directly print 3D nanostructurespractically and in large quantities. The window archetype critical forthe continuous printing in the '601 patent cannot be scaled tosub-micrometer scale because the diffusion distance of oxygen in theresin is about tens of micrometers.

Therefore, there is a need to scale the rate of 3D nanostructurefabrication by orders of magnitude in order to manufacture components ina manner that will allow for them to be distributed in next-generationtechnologies.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features, and advantages of the presentinvention will become more apparent when taken in conjunction with thefollowing description and drawings wherein identical reference numeralshave been used, where possible, to designate identical features that arecommon to the figures, and wherein:

FIG. 1 shows a prior art system for fabrication of monolithic polymeric3D parts.

FIG. 2A shows an arrangement for fabrication of 3D parts using anevanescent field to create a dead zone according to one embodiment.

FIG. 2B shows an arrangement for fabrication of 3D parts using a zoneplate lens to create a dead zone according to one embodiment.

FIG. 2C shows another arrangement for fabrication of 3D parts using azone plate lens to create a dead zone according to one embodiment.

FIG. 3 shows optical transitions in STED-based photoinitiation andphotoinhibition according to one embodiment.

FIG. 4 shows a calculation of the dead zone produced by the evanescentfield near the window-resin interface under the Kretschmannconfiguration according to one embodiment.

FIG. 5A shows an example design of the zone plates with two focallengths for two wavelengths wherein a shorter wavelength beam is focusedbehind the longer wavelength beam according to one embodiment.

FIG. 5B shows an example design of the zone plates with two focallengths for two wavelengths wherein a shorter wavelength beam is focusedbehind the longer wavelength beam according to one embodiment.

FIG. 6 shows example chemical structures for each of the threecomponents of the 3D nanoprinting system according to one embodiment.

FIG. 7A shows a photonic schematic of the arrangement of FIG. 2A.

FIG. 7B shows a photonic schematic of the arrangement of FIG. 2B.

FIG. 7C shows a photonic schematic of the arrangement of FIG. 2C.

DETAILED DESCRIPTION

For the purposes of promoting an understanding of the principles of thepresent disclosure, reference will now be made to the embodimentsillustrated in the drawings, and specific language will be used todescribe the same. It will nevertheless be understood that no limitationof the scope of this disclosure is thereby intended.

A novel arrangement is disclosed that can scale the rate of 3Dnanostructure fabrication of the prior art by orders of magnitude.According to one embodiment, an arrangement is disclosed for rapidlyprinting 3D nanostructures with feature resolution of ˜10s-100s nm(i.e., at a factor of ˜100-1,000 smaller than what is achievable usingthe current state-of-the-art rapid printing technology). The presentdisclosure is related to U.S. Pat. No. 9,205,601 to Desimone et al. Toprovide a dead zone for 3D nanoprinting, a photoinhibition method isused, which is similar to STimulated Emission Depletion (STED). TheSTED-based technique can inhibit photopolymerization at the nanoscale(2D), with resolution of ˜10s of nm and even below 10 nm. Moreover, thedisclosed arrangement is scalable—hundreds of parts can be printed inparallel. A low-cost ultraviolet (UV) light sources are used accordingto one embodiment. The arrangement according to the present disclosurecan: (1) provide a feature resolution two to 2-4 orders of magnitudesmaller than that of the process disclosed in the '601 patent; and (2)provide as a printing speed at least 2-3 orders of magnitude faster thanthe current 3D nanofabrication technology.

FIGS. 2A, 2B, and 2C provide schematics of the 3D nanoprintingarrangement 200 according to the present disclosure. A writing opticalbeam 202 (only shown as a UV laser beam as an instance in the figure butnot limited to a UV or a laser beam, moreover, an infrared light sourcecan be used for UV absorption via a multi-photon absorption process) isused for 3D printing through photopolymerization of the liquid resin204. The UV beam 202 is spatially modulated by a spatial light modulator206 (only shown as a digital micromirror device (DMD) as an instance butnot limited to a DMD) and the patterned UV beam is then projected ontoan array of Fresnel zone plates 208 (only one zone plate is shown, andonly shown as an instance in the figure but not limited to Fresnel zoneplates as light focusing devices) fabricated on a transparent window210. Each zone plate 208 functions as a miniature solid immersion lens,creating a de-magnified image at the location where it is desired forphotopolymerization to occur.

Photoinhibition technologies derived from STED are used to create apolymerization dead zone for continuous printing, as illustrated in FIG.3. An initiation beam 300 excites molecules to an excited state. In theabsence of other optical transitions, these excited states initiatepolymerization 302. When an inhibition beam 304 is present, it induces astimulated emission 306 that depletes the excited states (hence,Stimulated Emission Depletion—STED) and, thus, inhibits polymerizationand creates a dead zone. In some photo-chemical reactions STED is notinvolved, and the incident light can produce radicals that can inhibitpolymerization. According to one embodiment, an evanescent-typeconfiguration, as illustrated in FIG. 2A is used. In this configuration,the zone plate 208 projects a first photonic source beam 202 image intothe resin 204 to initiate photopolymerization, and a second photonicsource beam 212 of a different wavelength illuminates at an anglegreater than the critical angle of the window-liquid resin interface andexcites an evanescent field of a few hundred nm in depth (Further detailprovided below). This evanescent field creates a dead zone 214 rightbelow the image plane of the initiation beam to inhibit polymerization.Therefore, unlike any other STED-based 2D nanolithography, theSTED-based approach described herein is applied along the depthdirection in order to generate a dead zone for 3D continuouspolymerization. According to a second embodiment shown in FIG. 2B asarrangement 250, a Fresnel zone plate is used to focus thephotopolymerization beam 202 and inhibition beam 212 (only shown as aninstance in the figure but not limited to Fresnel zone plates as lightfocusing devices). The same zone plate is used to project a firstphotonic source beam 202 as the initiation beam for polymerization and asecond photonic source beam 212 as the inhibition beam for creating adead zone 214 right below (i.e. also along the depth direction) theimage plane of the initiation beam 202. The inhibition beam 202 can alsocarry images generated from the same or a second DMD 216 (only shown asa second DMD in FIG. 2B) for fine tuning the location and depth of theinhibition field and thus improving the fabrication resolution (seebelow for further detail). According to a third embodiment shown in FIG.2C as arrangement 270, the dead zone 214 is created using a photoabsorbing material whose penetration depth is wavelength dependent. Thisalso allows generation of a dead zone by the inhibition beam 212.Because the thickness of the liquid layer is a few hundreds of nm thick,a liquid resin flow cell can be used. In all embodiments, by pulling thefabricated part away from the printing zone and synchronizing thismotion with the projected initiation (and inhibition in FIG. 2B) lightbeam patterns, continuous printing of 3D nanostructures can be realized.

The evanescent-type arrangement (FIG. 2A) can define a dead zone with asharper transition to the polymerization zone over a distance of about100 nm, which provides high resolution in the depth direction normal tothe window surface. On the other hand, the zone plate projectionarrangement (FIG. 2B) and the use of wavelength dependent photoabsorbing material (FIG. 2C) may provide a thicker dead zone. Thereforeit is easier for the flow of the resin, and it also provides the freedomto generate the inhibition field at different distances relative to theinitiation field according to the required building parameters. It alsohas more flexibility when choosing the window materials as there is noneed to produce an evanescent field, and the numerical aperture (NA) ofthe zone plate can be made as large as possible (desirable for higherresolution). On the other hand, because the depth of the inhibitionimage is a few hundreds of nanometers, it requires more diligent effortsto improve the feature resolution along the depth direction such astrimming the depth of the initiation zone by carefully positioning theinhibition image with respect to the initiation image.

The disclosed 3D nanoprinter arrangement can be built on the frame of aninverted microscope, e.g., used for femtosecond laser (800 nm)two-photon 3D photopolymerization nanofabrication with additions oflasers and optical and opto-mechanical components. There are manyoptions of the wavelength for initiation and inhibition beams. Theinitiation beam can be continuous wave (CW) UV and visible light beams,or infrared (IR) femtosecond pulsed laser beams via a multiphotonabsorption process. Furthermore, the inhibition beam can also span fromthe near-IR to UV either through a STED process to terminatepolymerization as shown in FIG. 3, or a process that an inhibition beamproduces radicals that terminate polymerization or blocks the initiationbeam. The wavelength of the photoinhibition beam can be either longer orshorter than the photoinitiation beam. A wide array of laser sources canbe used, including 800 nm femtosecond and picosecond laser systems,which can be frequency doubled and tripled to 400 nm and 266 nm, UV CWlasers, and frequency doubled and tripled YAG and YLF lasers in thevisible and UV spectral range. These provide the flexibility ofwavelengths for which the photopolymers can be synthesized, and theinitiation beam and the inhibition beam wavelengths can be chosensufficiently apart to increase the fidelity of the printing process.Low-cost, high power UV CW sources at wavelengths such as 355 nm, 266nm, and 245 nm can also be used as a low-cost 3D parallel nanoprintingsystem. Other narrow or broad band light sources (including but notlimited to such as light emitting diodes, mercury lamps) with or withoutoptical filter can also be used.

The disclosed arrangements are particularly suitable for largethroughput scales. An array of the zone-plates or other focusing devicescan be fabricated on the window, allowing for large scale parallelprinting.

The dead zone for the disclosed arrangement are provided using anevanescent near-field or focusing both the photoinitiation beam and thephotoinhibition beam using the same zone plate, as shown in FIGS. 2A,2B, and 2C. Optical simulations can be performed with the measuredphotopolymer properties (vide infra) to estimate the power-dependenteffectiveness for creating the dead zone.

FIG. 4 illustrates a calculation of the dead zone produced by theevanescent field near the window-resin interface under the Kretschmannconfiguration. In this calculation, a thin metal or other photonics film(10 nm gold used in this case) is applied at the window interface whichserves as plasmonic material. Other materials (such as nano- ormicro-scale structured photonics thin film) can also be used to convertincident inhibition light into surface waves or other modes such aswaveguide modes that are trapped near the resin-window interface. Theresin typically has an optical refractive index of 1.5 or lower, and awindow material with higher refractive index is used to generate theevanescent field. A sapphire substrate and zirconia or diamond coatingsare good initial materials candidates for this application because theyhave indices of refraction of about 1.8, 2.2 and 2.5 in opticalfrequency respectively. When the incident angle of the photo-inhibitinglight is greater than the critical angle of total internal reflectionevanescent waves are excited with the momentum matching that of thesurface plasmon resonance. Under this condition, the incident energyefficiently excites propagating surface plasmons and the intensity ofthe reflected light decreases sharply. Because of strong fieldenhancement near the interface, the evanescent field can extend from thewindow to a distance of about 500 nm as shown in the calculations inFIG. 4. Outside this 500 nm dead zone, the inhibiting light intensityrapidly drops and polymerization can take place by using the zone plateto focus the photoinitiation beam at 500 nm from the window-resininterface. Further performance improvements are possible by optimizingthe thickness and the material of the metal film, within the thicknesslimit that allows majority of the photoinitiation light passing through.

It should be noted that it is possible to design the zone plate or otherfocusing devices to focus the initiation beam and the inhibition beam attwo separate locations along the beam propagation direction. As anexample, zone plates can be designed to focus light beams of differentwavelength in arbitrary order. FIGS. 5A and 5B show two representativeexample designs of the zone plates with two focal lengths for twowavelengths. In the first case a shorter wavelength beam is focusedbehind the longer wavelength beam (FIG. 5A), and in the second case thelonger wavelength beam is focused behind the shorter wavelength beam(FIG. 5B). The separation distance between the two beams in each case isalso adjustable as illustrated in FIGS. 5A and 5B. This will allowtrimming the depth of growth zone to improve the build resolution alongthe axial direction by carefully positioning the inhibiting beam withrespect to the initiating beam along the axial direction.

An important factor to the 3D nanoprinting process disclosed here is theuse of advanced organic molecular structures that are capable of beingconverted from a mobile, liquid-like resin state to a rigid, solid-likecrosslinked polymer state through a photoinitiated polymerizationmechanism, and in the meantime providing for photoinhibition at adifferent wavelength. Three major molecular components are required.First, the monomer to be polymerized is synthesized in a systematicmanner. Second, the photoinitiating species is chosen. Third, thephotoinhibiting species is chosen (it can be the same as the initiationspecies as shown in FIG. 3, or can be a different species to generateradicals to terminate polymerization). Importantly, photoinitiating andphotoinhibiting must have complementary absorption spectra. As such,very specific molecular design criteria (see FIG. 6 for example chemicalstructures) are required for each of the three components of the 3Dnanoprinting system. Triethylene glycol dimethacrylate (TEGDMA) is usedas it has a rather rapid photopolymerization and gel times at reasonablemonomer to photoinitiator concentrations and irradiation intensities.Moreover, for the applications of 3D nanostructures requiring specificproperties or multifunctional constitutive materials, because of therelative polar nature of the TEGDMA monomer and its rapid polymerizationkinetics, incorporation of other materials into the 3D-printed polymernanostructure could occur with relative ease.

The choice of the photoinitiating and photoinhibiting small moleculesfor the polymerization is important as the absorption of these materialswill dictate the wavelengths of light used during thephotopolymerization process and, thus, the ultimate scale of the3D-printed nanostructures. According to one embodiment thephotoinitiator system of comphorquinone (CQ) and 4-(dimethylamino)benzoate (EDAB) can be used as this system is known to absorb well atlonger wavelengths (the maximum in the absorption profile occurs nearthe wavelength λ=400 nm for the frequency doubled femtosecond laser beamwhile having relatively weak absorption in the ultraviolet region of theelectromagnetic spectrum. This complements the absorption spectrum(i.e., the absorption is negligible at λ>375 nm) of theinitially-selected photoinhibitor, tetraethylthiuram disulfide (TED);therefore inhibition of photopolymerization with wavelengths shorterthan 375 nm can be achieved. By extending the degree of r-conjugationwithin the photoinitiator molecular structure, the absorption spectrumcan be adjusted to specific wavelengths. Additionally, the addition ofspecific chemical group functionalities (e.g., mercaptofunctionalization) can alter the photoinitiating process in STED-basedlithography. Therefore, the absorption band of the photoinitiating andphotoinhibiting systems can be tuned either through the manipulation ofthe carbon-carbon bond structure or through the introduction of specificchemical groups along the backbone of these small molecule initiators.In turn, these chemical modifications will afford the manufacturingprocess to utilize shorter photoinitiating wavelength in deep UV (˜250nm) but much longer photoinhibiting wavelengths. Smaller dimensionality3D nanostructures and higher fidelity are thus possible during theprinting process.

Referring to FIGS. 7A, 7B, and 7C, photonic schematics are providedaccording to the present disclosure. FIG. 7A corresponds to FIG. 2A.FIG. 7B corresponds to FIG. 2B. FIG. 7C corresponds to FIG. 2C

Those skilled in the art will recognize that numerous modifications canbe made to the specific implementations described above. Theimplementations should not be limited to the particular limitationsdescribed. Other implementations may be possible.

1. A rapidly printing 3D nanostructures arrangement, comprising: a firstphotonic source configured to provide photoinitiation energy to apolymer medium via a dynamic light spatial modulation member to anexcited state to initiate polymerization; a second photonic sourceconfigured to selectively provide inhibition energy to the polymerizedmedium to a depleted state to inhibit polymerization thereby generatinga dead zone below a growth zone, wherein the dead zone allows continuous3D polymerization, wherein the first and second photonic sources areapplied to the polymer medium at substantially the same angle.
 2. Therapidly printing 3D nanostructures arrangement of claim 2, wherein thebeams of the first and second photonic sources pass through a focusingdevice prior to being projected on to the polymer medium, but atdifferent depths.
 3. The rapidly printing 3D nanostructures arrangementof claim 2, wherein the beams of the first and second photonic sourcespass through an array of lenses prior to being projected on to thepolymer medium.
 4. The rapidly printing 3D nanostructures arrangement ofclaim 2, wherein the photo initiation beam and the photo inhibition beamhave different penetration depths.